Expansion chambered, fail-safe muffler

ABSTRACT

Muffler for air-exhausts of pneumatically operated equipment in which sound is muffled by passage of the air from a relatively unrestricted first domed expansion chamber through a first disseminator into a silencing chamber and thence diffused through porous side of the silencing chamber. The end of the silencing chamber opposite the first disseminator is partly closed by a second disseminator opening into a second domed expansion chamber having an opening to the atmosphere.

United States Patent Gibel 51 Sept. 5, 1972 [54] EXPANSION CHAMBERED, FAIL-SAFE MUFFLER [72] Inventor: Stephen J. Gibel, 5846 Edgerton Road, North Royalton, Ohio 44133 [22] Filed: Aug. 26, 1971 [21] Appl. No.: 175,175

Related US. Application Data [63] Continuation-impart of Ser. No. 162,785, July [52] US. Cl ..181/36 A, 181/55, 181/61, 181/69, 181/57, 181/37, 181/56, 181/72 [51] Int. Cl. ..F01n l/l0, FOln 7/18 [58] Field of Search ....l8l/35 A, 36 R, 59, 36 A, 40, 181/48, 42, 50, 47, 55, 61, 57, 69, 68, 60,

[56] References Cited UNITED STATES PATENTS 2,039,800 5/1936 Jack ..181/48 6/1952 -Gibel ..181/60 2,600,236 3,339,668 9/1967 Trainor ...l8 l/36 A 3,380,553 4/1968 Gibel ..181/60 FOREIGN PATENTS OR APPLICATIONS 841,828 7/1960 Great Britain .l81/59 Primary Examiner-Robert S. Ward, Jr. Attorney-Ely, Golrich & Flynn [57 ABSTRACT Muffler for air-exhausts of pneumatically operated equipment in which sound is muffled by passage of the air from a relatively unrestricted first domed expansion chamber through a first disseminator into a silencing chamber and thence diffused through porous side of the silencing chamber. The end of the silencing chamber opposite the first disseminator is partly closed by a second disseminator opening into a second domed expansion chamber having an opening to the atmosphere.

7 Claims, 3 Drawing Figures EXPANSION CHAMBERED, FAIL-SAFE MUFFLER CROSS-REFERENCES TO RELATED APPLICATIONS This invention is an improvement upon those of the types shown in my US. Pat. No. 3,380,553, issued Aug. 30, 1968, and in my application for Expansion Chambered, Pressure Relief Muffler, Ser. No. 162,785, filed July 15, 1971, of which this application is a continuation-in-part.

This invention relates to improvements in mufflers for'the exhausts of pneumatically operated tools, cylinders, and like equipment, particularly pneumatically operated clutches, brakes, and valves in which the back-pressure of the exhaust line must not exceed prescribed minimum pressures.

Mufflers of the above-described type have heretofore been comprised essentially of a head having a plurality of chambers therein for turbulent expansion of the exhaust gases, said chambers being separated by a disseminator plate from a following silencing chamber in which the expanded air is discharged through a cylindrical side wall of fibrous or like porous material retained against the head by a suitable end cover. As initially installed such mufflers are highly efficient silencers dissipating the fluid energy of such air which, if unmuffled would exhaust the air at an intolerable noise level. Unfortunately the exhaust air for many pneumatically operated tools and equipment contains entrained fine mists of liquids and vapors which can clog the interstices of the porous walls of the silencing chamber. This can cause the eventual build-up of back pressures which at least slows down and impairs the efficiency of the operation of the pneumatically operated or controlled devices but which may not be necessarily noticeable until the speed of operation is appreciably slowed; in the case of equipment depending upon the timed operation of pneumatically operated clutches, brakes, or valves, such a slow-down may even cause malfunction of the equipment. Even before any such slow-down, the entire muffler usually should have been replaced either by a new muffler or one which has been re-conditioned by replacement of the clogged sidewall. Due to the intolerable noise of the unmuffled exhaust, however, any such replacement, whether before or after appreciable slow-down, must normally be postponed until the end of the shift or other production period in which operation is shut down.

It is an object of this invention to provide an improved muffler of the type described which emits an audible warning that the muffler or its silencing element should be replaced.

It is an object and advantage of this invention that until the muffler or its acoustical silencing element is replaced, it will continue to operate without creating back-pressures in the exhaust lines exceeding the tolerances allowed by the pneumatic devices and that such continued operation is not dependent upon the operation of any moving parts or elements. Accordingly, mufflers made according to this invention are termed fail-safe.

The present invention resides in certain heretofore unobvious constructions and combinations and revisions and rearrangements of parts, providing a more efficient operation and economical construction; its

further advantages will be apparent from the following description, claims, and drawings, in which:

FIG. 1 is an end view ofthe domed head of a muffler made according to this invention.

FIG. 2 is a cross-section taken along the line 2--2 of FIG. 1.

FIG. 3 is an end view taken along the line 3-3 of' FIG. 2.

Referring to the drawings, a muffler made according.

nected thereby by a suitable fitting. The circumference.

of the cover 10 constitutes an internal flange 12 providing a seat for a disseminator sheet 13 and the body 20. The seat of the flange 12 is axially spaced from the.

outer wall 14 of the cover 10 to provide an expansion chamber 15 between the. sheet 13 and the wall 14. Except for the internal bosses 16 tapped to receive the threaded ends of the tie bolts 17 and the fillet connecting the wall 14 to the flange 12, the expansion chamber- 15 is a substantially unrestricted cylindrical volume. For effective operation it has been found that the proportion of the axial length to the internal diameter of the chamber may be at least in the order of 123.5 and preferably in the order of 1:5. Particularly if the effective limits of the area of the disseminator sheet'to the base of the inlet pipe fitting on which the boss 11 is mounted are observed, a proportion of the axial length of the chamber 15 to its internal diameter greater than the order of 1:10 will unduly constrict the desired expansion of exhaust air in the chamber 15 The disseminator sheet 13 may be either a disk of perforated metal, as shown, or of open-mesh screen of heavy wire. If of perforated metal, the area of the openings with respect to the total area of the sheet measured at the inside diameter of the porous sleeve 21' or the seat of the flange 12 (whichever is smaller) is preferably approximately 50 percent. It may be as lowas 30 percent (a lesser percentage materially constricts the flow of air through the sheet) and as high as approximately percent (in order to provide sufficient strength and an adequate pressure drop across the sheet). If wire mesh is used instead of a perforated metal sheet, the same ratios of open area to the effective total area of the disseminator should be observed; this may be obtained, for example, with screen as fine as 14 mesh screen of 0.028 inches wire or coarser screen. The proportions of the total effective area of the. sheet 13 to the bore of the fitting received by the boss 11 has also been found critical. A ratio of approximately 13:1 has been found preferable with a lower limit of 10:1 necessary for satisfactory operation and an upper limit of 20:1 dictated by the economy of the size of the muffler for the amount of exhaust air which can be delivered into the domed cover 10 at normal low exhaust line pressures.

The body 20, defining a silencing chamber 25', is comprised of a tubular wall 21 of highly porous acoustical material such as loosely felted cellulosic fibers (bonded together to the extent necessary for mechanical strength by suitable resinous binders) providing a tortuous path for the exhaust air through the wall 21. The axial length of the wall is dictated by its porosity, and should not provide a pressure drop materially greater than that across the plate 13; the wall should also be thick enough to reduce the sound level to approximately that of the surrounding atmosphere. To protect the relatively soft and porous wall 21 and provide strength for the axial load imposed by the tie bolts 17, an outer covering of perforated metal or screen 22 is provided.

The end closure 30 for the silencing chamber 25 is a partial rather than a complete closure; it is preferably a domed structure similar to the head 10, except for differences in minor and major details described below. Thus, it has an end wall 34 axially spaced from an internal flange 32 receiving the body 20 and internal bosses 36 similar to the bosses 16 except that the bosses 16 are simply drilled to receive the head ends of tie bolts 17 to permit the assembly of the unit (and its disassembly to replace the acoustical element 21). Secured between the end of the body 20 and the seat of the internal flange 32 is a disseminator 33 corresponding to the disseminator l3 and likewise preferably of perforated metal or open-mesh wire screen having the same ratio of openings to total areas as in the disseminator 13. Also, the axial spacing between the disseminator 33 and the end wall 34 is similar to that of the spacing between the disseminator 13 and wall 14 whereby a second substantially unrestricted expansion chamber 35 corresponding to the expansion chamber 15 is provided.

The major and significant difference between the enclosure 30 and the head is that, instead of being provided with a central internally threaded boss 11, as is the head 10, the closure 30 is drilled to provide an unrestricted central opening 31. The proportion of the area of the opening31 to the area of the bore of the pipe or fitting received in the boss 11 can be significant for function of the muffler as described below. To avoid a restriction on exhaust gases entering the muffler in the event the wall 21 becomes completely clogged, the area of the opening 31 should be larger than the bore of the pipe or fitting received in the boss 1 1 (hereafter the entrance bore area). A ratio of the area of the opening 31 to the entrance bore area in the order of 2:1 as been found preferable; larger ratios of the area of the opening 31 to the entrance bore area do not materially increase the fail-safe advantage of the muffler and diminish the sound-muffling effectiveness of the expansion chamber 35 to asymptotic values as the ratio approaches 4:] or larger.

The above-described muffler, with its fail-safe" result, functions as follows: Exhaust air enters the boss 11 with substantial noise-producing kinetic energy. This energy and noise is lessened at a primary stage by the effectively unrestricted and relatively non-turbulent expansion into the first expansion chamber and, at a second stage, by its passage into the silencing chamber and at a third stage as the expanded air in the silencing chamber 25 is widely and gently dispersed through the body 20. This third stage would be the final and conclusive stage if the end of the body were completely closed as, for example, it is before the pressure-relief means functions in the generally corresponding structure disclosed in my copending application Ser. No. 162,785, for Expansion-chambered, Pressure Relief Muffler.

The function of mufflers made according to this invention turns upon my discovery that, in mufflers of the type providing the three stage silencing as above described, it is not necessary that the end of the silencing chamber be completely closed to obtain substantial and effective noise reduction; rather, such substantial reduction can be obtained with a partial closure of the silencing chamber by an end closure such as the closure 30 above described. Particularly when the wall 21 is fresh and wholly unclogged, the degree of silencing obtained by use of the partial end closure 30, while not equivalent to that which would be obtained if the end were completely closed, can be in the order of to percent as effective, wholly out of proportion to that which would be expected, especially in view of the fact that the opening 31 allows substantially a zero pressure static differential from ambient atmospheric pressure throughout the interior of the muffler and particularly in the silencing chamber 25. A muffler made according to this invention is, accordingly, generally highly acceptable for noise reduction in most locations and is highly advantageous where less than optimum reduction of noise levels must be tolerated for a fail-safe operation of machinery and equipment at such locations.

The fail-safe function is as follows: When the acoustical wall material 21 is fresh and unclogged, exhaust air in the chamber 25 disperses through the wall 21 and also escapes through the opening 31, but that which escapes through the opening 31 does so with little kinetic energy and emission of sound. This may or may not be due to the function of the disseminator 33 in reflecting back to the wall 21 such sound waves and the absorption in the wall 21 of their energy as it passes from the disseminator 13 to the disseminator 33 and/or the function of the second expansion chamber 35 in dissipating the sound energy of the exhaust passing into it through the interstices of the second disseminator 33.

As effectiveness of the wall 21 decreases due to its becoming gradually clogged and loaded vwith the in evitable entrained moisture and lubricants in the exhaust and which the porous acoustical material filters out, its silencing function is correspondingly increasingly taken over by the second disseminator 33 and ex pansion chamber 35. These elements are not as effective as the acoustical material of the wall 21 and thus take-over due to the deterioration of the acoustical material and the need for its replacement are signalled by the increase in noise emitted by the muffler. But even if the acoustical material should fail completely because it became fully impregnated with the gums which form from the mixed water and lubricants, the complete take-over of sound-muffling functions by the closure 30 would be accomplished without creating a back-pressure that would impair the safe operation of the pneumatic equipment to which the muffler is attached. I

The embodiment of the invention illustrated in the accompanying drawings shows it in a horizontal position, in which it must necessarily be mounted on many pneumatic devices. in a Fail-safe muffler made ac cording to this invention, the life of its wall material 21 will be prolonged if the muffler can be positioned so that its axis is vertical, thereby allowing at least some of the entrained droplets which separate from the air within the chamber 25 to fall to the disseminator 33 and drain through the opening 31.

This invention is not limited to the specific embodiment disclosed, but may be varied within the scope of the following claims.

What is claimed is:

l. A fail-safe muffler for the exhaust of a pneumatic device whose operation is affected by the back-pressure of its exhaust comprising a head member by which the muffler is connected to the tubular exhaust of a pneumatic device and providing an inlet to the interior of said muffler from said exhaust, a body connected to said head comprised of a tubular wall having a sufficient area and porosity to allow, at least initially, dispersion of the exhaust therethrough, and a partial end closure for said body to provide a silencing chamber within said body, said end closure comprising a disseminator sheet providing openings from said silencing chamber to an expansion chamber, said expansion chamber including a wall spaced from said disseminator sheet and having a substantially unrestricted opening to the ambient atmosphere, the area of said opening in said expansion chamber being greater than the entrance bore of said inlet to said muffler.

2. A muffler as defined in claim 1 in which the pro- 8 portion of the area of said disseminator sheet to said entrance bore area ranges between 10 and and the proportion of the area of the openings in said disseminator sheet to its total area ranges between 50 to 70 percent.

3. A muffler as defined in claim 1 in which the area of said disseminator sheet having openings from said silencing chamber to said expansion chamber is a disk and said wall having an opening therein is axially spaced from said disk area a distance ranging between l:4 and 1:10 of the diameter of said disk, said wall extending at its periphery to said disk area to provide a substantially unrestricted cylindrical expansion chamber between said disseminator sheet and said wall.

4. A muffler as defined in claim 3 in which the proportion of the area of said opening in said wall spaced from said disseminator sheet with respect to the entrance bore area of said inlet ranges from 1.5 to 4, whereby, when the tubular porous wall of said body becomes clogged, exhaust may escape from said silencing chamber through said partial end closure, said par tial end closure maintaining the static pressure within said silencing chamber at substantially the pressure of the ambient atmosphere.

5. A muffler as defined in claim 1 in which said expansion chamber is a second expansion chamber, the disseminator sheet thereof is a second disseminator sheet, and said head member includes a first expansion chamber defining the end of said silencing chamber opposite said second expansion chamber, said first expansion chamber including a first disseminator sheet axi ally spaced from the inlet to said head member to define a first expansion chamber, whereby exhaust entering said inlet passes through said first expansion chamber to said silencing chamber and a portion of said exhaust entering said silencing chamber at least initially is dispersed through said porous tubular wall of said body and the balance passes through said second I disseminator sheet to said second expansion chamber and thence to the ambient atmosphere through the opening in the wall of said end closure 6. A muffler as defined in claim 5 1n which the proportion of the area of said first disseminator sheet to said entrance bore area ranges between 10 and 20 and the proportion of the area of the openings in said first disseminator sheet to its total area ranges between 50 to percent.

7. A muffler as defined in claim 6 in which the area of said first disseminator sheet having openings to said silencing chamber from said first expansion chamber is a disk and said inlet to the muffler is a wall axially spaced from said disk area a distance ranging between 1:4 and 1:10 of the diameter of said disk, said wall extending at its periphery to said disk area to provide a substantially unrestricted cylindrical first expansion chamber between said first disseminator sheet and said wall. 

1. A fail-safe muffler for the exhaust of a pneumatic device whose operation is affected by the back-pressure of its exhaust comprising a head member by which the muffler is connected to the tubular exhaust of a pneumatic device and providing an inlet to the interior of said muffler from said exhaust, a body connected to said head comprised of a tubular wall having a sufficient area and porosity to allow, at least initially, dispersion of the exhaust therethrough, and a partial end closure for said body to provide a silencing chamber within said body, said end closure comprising a disseminator sheet providing openings from said silencing chamber to an expansion chamber, said expansion chamber including a wall spaced from said disseminator sheet and having a substantially unrestricted opening to the ambient atmosphere, the area of said opening in said expansion chamber being greater than the entrance bore of said inlet to said muffler.
 2. A muffler as defined in claim 1 in which the proportion of the area of said dissEminator sheet to said entrance bore area ranges between 10 and 20 and the proportion of the area of the openings in said disseminator sheet to its total area ranges between 50 to 70 percent.
 3. A muffler as defined in claim 1 in which the area of said disseminator sheet having openings from said silencing chamber to said expansion chamber is a disk and said wall having an opening therein is axially spaced from said disk area a distance ranging between 1:4 and 1:10 of the diameter of said disk, said wall extending at its periphery to said disk area to provide a substantially unrestricted cylindrical expansion chamber between said disseminator sheet and said wall.
 4. A muffler as defined in claim 3 in which the proportion of the area of said opening in said wall spaced from said disseminator sheet with respect to the entrance bore area of said inlet ranges from 1.5 to 4, whereby, when the tubular porous wall of said body becomes clogged, exhaust may escape from said silencing chamber through said partial end closure, said partial end closure maintaining the static pressure within said silencing chamber at substantially the pressure of the ambient atmosphere.
 5. A muffler as defined in claim 1 in which said expansion chamber is a second expansion chamber, the disseminator sheet thereof is a second disseminator sheet, and said head member includes a first expansion chamber defining the end of said silencing chamber opposite said second expansion chamber, said first expansion chamber including a first disseminator sheet axially spaced from the inlet to said head member to define a first expansion chamber, whereby exhaust entering said inlet passes through said first expansion chamber to said silencing chamber and a portion of said exhaust entering said silencing chamber at least initially is dispersed through said porous tubular wall of said body and the balance passes through said second disseminator sheet to said second expansion chamber and thence to the ambient atmosphere through the opening in the wall of said end closure.
 6. A muffler as defined in claim 5 in which the proportion of the area of said first disseminator sheet to said entrance bore area ranges between 10 and 20 and the proportion of the area of the openings in said first disseminator sheet to its total area ranges between 50 to 70 percent.
 7. A muffler as defined in claim 6 in which the area of said first disseminator sheet having openings to said silencing chamber from said first expansion chamber is a disk and said inlet to the muffler is a wall axially spaced from said disk area a distance ranging between 1:4 and 1:10 of the diameter of said disk, said wall extending at its periphery to said disk area to provide a substantially unrestricted cylindrical first expansion chamber between said first disseminator sheet and said wall. 